1. Field of the Invention
The present invention relates to adsorbent materials for use in adsorption chillers, and particularly to a composite adsorbent for an adsorption chiller, the composite adsorbent being formed from multi-walled carbon nanotubes incorporated into a MIL-101(Cr) metal organic framework.
2. Description of the Related Art
Adsorption chillers combine an adsorbent with a refrigerant, allowing the chiller to use heat to provide a cooling effect. This heat, typically in the form of hot water, may come from any number of industrial sources, including waste heat from industrial processes, prime heat from solar thermal installations, or from the exhaust or water jacket heat of a piston engine or turbine.
Although there are similarities between absorption and adsorption refrigeration, absorption refrigeration utilizes a process in which a refrigerant fluid is dissolved by a liquid or solid sorbent, while adsorption refrigeration utilizes a process in which the refrigerant fluid adheres to the surface of the sorbent. Typical refrigerant/absorbent pairs used in absorption chillers include ammonia/water or water/lithium bromide solution, while typical refrigerant sorbent pairs in adsorption chillers include water/silica gel or water/zeolite. The adsorption chamber of the adsorption chiller is filled with a solid material (for example, a zeolite or silica gel) which, in its neutral state, has adsorbed the refrigerant. When heated, the solid desorbs (i.e., releases) refrigerant vapor, which subsequently is cooled and liquefied. This liquid refrigerant then provides its cooling effect at the evaporator, by absorbing external heat and turning back into a vapor. In the final stage, the refrigerant vapor is re-adsorbed into the solid.
Conventional small-scale solar adsorption chillers generally employ silica gel/water or zeolite/water working pairs, due to their relatively high levels of mesoporosity and water affinity. However, the coefficient of performance (COP) and specific cooling power (SCP) evaluated for an adsorption chiller using these adsorbent/adsorbate pairs make their use feasible only for small scale use, since both the COP and SCP are far too small for practical use in a larger scale system, such as for commercial or industrial applications.
Thus, a composite adsorbent for an adsorption chiller solving the aforementioned problems is desired.